Epson LQ-870 Service Manual page 57

REV.-A
Location
2 C
4B
PROM 3A
RAM 4A
5A
MROM
( M a s k R O M ) 2 A
EEPROM 5c
V r e f C i r c u i t 1C
TL43 1
Table 2-5. Functions of the Main IC and Circuits
Receives data from the host computer and loads the data to the input buffer in
RAM (under interrupt processing control). Expands the input data held in the
buffer to create image data. Loads this image data to the image buffer in RAM.
Transfers the image data to the printhead drive circuit. Also controls various parts
of the printer mechanism, such as the motors.
This gate array consists of seventeen components configured on a single chip:
Memory Management Unit
Wait Control Unit
Refresh Control Unit
Program ROM Select Unit
Centronics I/F Control Unit
Option Control Unit
Panel Control Unit
EEPROM Control Unit
General Output Unit
HPW Differential Unit
HPW Pulse Limit Unit
Bit manipulation unit
Head Control Unit
Internal Clock Generate Unit
Internal I/O and MMIO Decode Unit
Output Data Multiplex and input Data Latch Unit
This is a drive circuit for the printhead. It consists of six chips.
The PROM contains the program that runs the CPU.
The RAM contains the CPU working area and the various buffers. (5A is not used
and not installed in the 80-column printer.)
The mask ROM contains the character design (also called the character
generator).
The EEPROM is an electronically writable and erasable ROM that contains infor-
mation such as the top-of-form position.
This circuit generates the reference voltage used irrthe A/D converter in the CPU.
Functions
2-16